In electrophotographic (EP) copiers and/or printers, contrast density and color balance (in color machines) can be adjusted by changing certain process control parameters such as primary voltage V.sub.O, exposure E.sub.O, development station bias voltage V.sub.B, the concentration of toner in the development mixture, and the image transfer potential.
Control of such EP parameters is often based on measurements of the density of a toner image in a test patch. Typically, the test patch can be recorded on an area of the electrophotoconductive imaging member between adjacent image frames and developed. The developed density of the patch can be measured and adjustments to EP set points made accordingly.
A problem associated with making such adjustments is that in attempting to maintain a constant density for say D.sub.MAX (maximum density areas) variability in lighter density steps can result due to changes in relative humidity. As is known, changes in relative humidity can affect charge to mass ratio (Q/m) of developers and affect primary charger performance. In examining the problem, the inventors have noted that since it is desirable that development station bias potential V.sub.B follow primary film voltage V.sub.O, an error in determining set point for primary film voltage can cause an error in the bias voltage setting to the development station V.sub.B which in turn causes lighter density steps to deviate from aim density.
It is, therefore, an object of the invention to provide for EP process control wherein parameters in the EP process are adjusted to ensure satisfactory consistency of density for D.sub.MAX as well as lighter density steps.